God Is Unchanging.
Jesus Christ is the same yesterday, today, and forever. Hebrews 13:8 NKJV
Jesus Christ the same, etc. The only way by which we can persevere in the right faith is to hold to the foundation, and not in the smallest degree to depart from it; for he who holds not to Christ knows nothing but mere vanity, though he may comprehend heaven and earth; for in Christ are included all the treasures of celestial wisdom. This then is a remarkable passage, from which we learn that there is no other way of being truly wise than by fixing all our thoughts on Christ alone.
Now as he is dealing with the Jews, he teaches them that Christ had ever possessed the same sovereignty which he holds at this day; The same, he says, yesterday, and today, and forever. By which words he intimates that Christ, who was then made known in the world, had reigned from the beginning of the world, and that it is not possible to advance farther when we come to him. Yesterday then comprehends the whole time of the Old Testament; and that no one might expect a sudden change after a short time, as the promulgation of the Gospel was then but recent, he declares that Christ had been lately revealed for this very end, that the knowledge of him might continue the same for ever.
It hence appears that the Apostle is not speaking of the eternal existence of Christ, but of that knowledge of him which was possessed by the godly in all ages, and was the perpetual foundation of the Church. It is indeed certain that Christ existed before he manifested his power; but the question is, what is the subject of the Apostle. Then I say he refers to quality, so to speak, and not to essence; for it is not the question, whether he was from eternity with the Father, but what was the knowledge which men had of him. But the manifestation of Christ as to its external form and appearance, was indeed different under the Law from what it is now; yet there is no reason why the Apostle could not say truly and properly that Christ, as regarded by the faithful, is always the same. - John Calvin